1. Field of the Invention
The present invention relates to lubricating engines using formulated lubricating oils to reduce deposit formation and friction in the engine.
2. Description of the Related Art
Engine oils are formulated for the purpose of reducing friction in the engine, engine cleanliness, e.g. deposit control, control of wear, corrosion and rust in the engine. To accomplish this goal the engine oil contains numerous and various additives including friction reducers, detergents, dispersants, extreme pressure additives, viscosity index improvers, and oxidants.
Of significant concern is the reduction of friction in engines so as to improve fuel economy necessitating the use of lower viscosity lubricating oil base stocks while also meeting the competing requirements of maintaining sufficiently high lubricating oil film thickness at high operating temperature to avoid incidental breakdown of the oil film under boundary conditions while still maintaining low wear over a wide range of temperatures.
The principal anti-wear additive for engine oils has been and is zinc dialkyl dithiophosphate (ZDDP); however, while ZDDP is typically used in the lubricating oil at a sufficient concentration to provide a phosphorus content of 0.08 wt % or more to pass industry standard tests for anti-wear performance, such high phosphorus content in the oil can result in deactivation of emission control catalysts used in automotive exhaust systems if and when engine oil migrates into the combustion chamber and is burned and becomes part of the exhaust gases. Thus, it is desirable to reduce the amount of phosphorus containing additive in the lubricating oil.
WO 2007/127836 is directed to a molybdenum-free lubricating composition comprising an anti-oxidant additive composition based on a combination of (1) alkylated diphenyl amine; (2) a polyamine dispersant; and (3) a concentration of monoglyceride and ethoxylated amide. Preferably the monoglyceride ethoxylated amide combination is borated which permits a reduction in the phosphorus levels in the lubricating oil to below 0.08 wt %, or even phosphorus free. Preferably the borated monoglyceride ethoxylated amide is Vanlube® 289. Other additives may be present including detergents such as the generally disclosed sulfonates, phenates and salicylates, with sulfonates being identified as preferred.
U.S. Application 2004/0138073 is directed to an additive for imparting anti-wear properties to a lubricant. The additive is based on a combination of an organoborate ester composition and one or more sulfur- or phosphorus-containing compounds or a non-sulfur molybdenum compound. The additives which are said to show a synergistic effect in combination with the borate ester composition include dithiophosphates such as ZDDP. The preferred borated ester composition is the reaction product obtained by reacting 1 mole fatty oil with about 1.0 to 2.5 moles diethanolamine followed by subsequent reaction with boric acid. The formulation of the references can contain detergents including metal salts of sulfonates, carboxylates, phenates and salicylates with preferred detergent being overbased organic salts of sulfonates.